Congo Chimps Harvest Ants Sustainably

Chimpanzees in the wild use specialized “tool kits” to forage food, it is known. Scientists reported earlier this year that chimps raiding beehives used several tools in a single tool-using episode and could also use a single tool for many different purposes. Now the same researchers report that not only do chimps use specialized tool...

September 15, 2009

Chimpanzees in the wild use specialized “tool kits” to forage food, it is known.

Scientists reported earlier this year that chimps raiding beehives used several tools in a single tool-using episode and could also use a single tool for many different purposes.

Now the same researchers report that not only do chimps use specialized tool kits to forage for army ants, but they are selecting tools and techniques that will not overly disturb and cause the ants to abandon the area–a sustainable method of harvesting that secures a renewable source of food.

“After spending a collective 111 months in the Goualougo Triangle, the team recovered 1,060 tools and collected 25 video recordings of chimpanzees using them to forage for army ants,” said a statement about the research by Washington University.

“It is already known that chimpanzees use tools when foraging for honey or collecting termites. However, the variation in techniques and the relationship between the ants and the chimpanzees has perplexed scientists for decades,” the university added.

“The use of tool sets is rare and has most often been observed in great apes,” Sanz said . “Until now there have been no reports of regular use of more than one type of tool to prey upon army ants.

“In other studies, based across Africa, chimpanzees have been seen to prey on army ants both with and without tools, and it was inexplicable why some chimpanzees used different techniques to gather the same prey.”

The average number of tools recovered by the team at each site was 3.37, while 36 percent of recovered tools sets contained two types of tools, nest-perforating tools like (woody saplings) and ant-dipping probes (such as herb stems).

Ant-dipping probes are the most commonly observed method of catching army ants, the scientists found. “The chimpanzee inserts a probe into a nest or column of ants and gathers the individuals who stream up the tool.”

Perforating tools are used to open nests so the chimpanzee can gather the ants within.

Adult male chimpanzee uses a tool set when visiting an army ant nest. He first uses a sapling with leafy branches intact on the unused end to perforate the nest, and then follows with an herbaceous dipping wand.

“While the tools sets observed during this study were similar to other recorded tools, this research suggests that chimpanzees are selecting tools depending on the characteristics of the ant species they are foraging,” Washington University said.

“There are several varying species of ants found throughout the triangle, but their characteristics can be divided into two categories, epigaeic or intermediate.

“Epigaeic ants have longer legs so can run faster and can inflict a more painful bite. They forage on the ground and in the vegetation and when attacked the workers counter-attack in large swarms.

“Intermediate species forage only in the leaf litter and withdraw into underground tunnels or into the leaf litter when attacked.”

Preventing an ant counter-attack

Chimpanzees that harvest ants simply by raking a nest open with their hands cause a massive counter-attack from the ants, Washington University said. “This results not only in bites but the attack may provoke the ants to migrate and build a new nest at a different location.

“However, by using the perforation tools the chimps can entice the ants out and can allow the insertion of the second tool for dipping.

“This not only reduces the ant’s aggressive behaviour but may also be a ‘sustainable harvesting’ technique as the ants will stay in that location allowing the chimpanzees to revisit this renewable source of food.”

Tool set used by chimpanzees to prey upon army ants in the Goualougo Triangle, Republic of Congo. The top two tools are herbaceous dipping probes. The bottom tool is a perforating tool with the leafy branches intact at one end. Above the perforating tool is a measuring tape totaling about 8 inches in length.

The chimpanzees practise recycling by recognising tool forms and re-using tools which have been discarded by other individuals during previous visits, Washington University added..

“It has only recently been discovered that these particular chimpanzees use several different types of tool sets which could be their cultural signature of sorts,” concluded co-author David Morgan, research fellow at Lincoln Park Zoo. “There is an urgency to learn about these behaviours as the existence of the apes in the Congo Basin is threatened by commercial logging, bushmeat hunting, and emerging diseases.”

The research was funded by the National Geographic Society’s Committee for Research and Exploration, the U.S. Fish and Wildlife Service, Columbus Zoological Park, Brevard Zoological Park, and Lowry Zoological Park.

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